1. Technical Field
The present invention generally relates to hydraulic actuators for applying impulse to a mass in a collision test so that the mass moves at a predetermined speed and methods of operating the hydraulic actuators and, more particularly, to a three-stage hydraulic actuator configured such that compressed oil is supplied into an acceleration chamber through a distributing orifice that opens when an acceleration piston moves forward, whereby the acceleration piston accelerates a mass, and to a method of operating the three-stage hydraulic actuator.
2. Description of the Related Art
Shock test apparatuses for use in shock tests include an actuator for accelerating a mass in a short time and moving the mass at a predetermined speed to simulate shock applied to a target.
For instance, such an actuator is designed such that a piston is slidably installed in a cylinder. When hydraulic pressure is supplied into the cylinder, the piston pushes the mass and thus accelerates it.
As such, the mass can be accelerated and moved at a predetermined speed by applying hydraulic pressure to the mass and pushing it. In this way, shock tests for simulating actual conditions can be conducted.
To increase the speed of the mass, the speed of the piston must be increased to a sufficient degree. For this, the magnitude of supplied hydraulic pressure must be increased to a desired degree. In addition, hydraulic pressure must be supplied in a short time.
However, increasing hydraulic pressure to push the piston is limited. Give this, methods such as increasing the capacity of a pressure accumulator or increasing the lengths of the cylinder and the piston have been used. In this case, a comparatively high flow rate is required to move a heavy mass at a high speed. Increases in size and length of the cylinder and the piston and use of several large pressure accumulators cause a problem of an excessive increase in size of equipment.